14 DR. E. KLEIN. 



ness, and to avoid all possible contamination. Immediately 

 before turning off the flame of the burner, and while the fluid 

 is still boiling, I place over the mouth of the flask a cotton- 

 wool cap, and keep this pressed over the mouth and upper 

 part of the neck of the flask by an inverted beaker pushed 

 firmly over it. The flask is then placed into an incubator, 

 and kept here at a temperature of about S2° — 35° C. After 

 two or three days the flask, plugged but without the cotton- wool 

 cap, is again placed over the gas-flame, and the broth subjected 

 to boiling for five to ten minutes. While still boiling the 

 cotton-wool cap and beaker are placed over the mouth and 

 neck, and the flame is turned ofi". Such a flask with broth 

 may now be considered absolutely sterile; it may be kept in 

 the incubator for weeks and months — it will always remain 

 absolutely limpid and free of any organisms. Such broth will 

 in the following be always spoken of as " sterile pork broth." 



This broth £ use either as such, i. e. as pure broth, or in 

 combination with gelatine, as " gelatine pork," in order to have, 

 as recommended by Koch (I. c), a nourishing material, not of 

 fluid but of solid consistency. I consider, with many others, 

 this method of Koch's, viz. of using gelatine as an admixture 

 to a nourishing fluid, and thus converting it into a solid state, 

 a very great advance indeed in the methods of cultivating 

 bacteria, especially in securing pure cultivations not contami- 

 nated accidently, for then the sowing of a particular species 

 of bacterium is possible in a particular spot or spots, the 

 growth and progress can be easily watched and controlled, 

 and accidental contaminations can be readily recognised ; but 

 I shall show below that it is quite possible also without the 

 gelatine admixture after the method I use to be almost abso- 

 lutely guarded from accidental contamination, i.e. to have 

 pure cultivations. Koch has very minutely described the ad- 

 vantages of the gelatine method and his modus procedendi, 

 and he has given numerous photographic illustrations of 

 various species of bacterium in pure cultivations eff'ected by 

 his gelatine method. 



Koch recommends, in order to solidify the nourishing 



